1. Field of the Invention
Exemplary embodiments of the present invention relate to an O2 purge control method and an exhaust system for two type catalysts composed of WCC and UCCfh, and more particularly, to an O2 purge control method and an exhaust system for two type catalysts having catalysts arranged in two rows which may greatly improve reduction efficiency of catalytic oxidation atmosphere so as to remove NOx by increasing an O2 purge quantity immediately after a fuel-cut and prevent a generation of emissions such as CO and HC of the UCC arranged after the WCC.
2. Description of Related Art
Generally, it is very important to reduce NOx and CH/HC due to environment regulation for exhaust gas. To this end, a catalyst is used in an exhaust system of a gasoline vehicle to reduce NOx and CO/HC.
As the example, a warm up catalytic converter (hereinafter, referred to as WCC) and a under floor catalytic converter (hereinafter, referred to as UCC) may be installed before and after an exhaust pipe.
Generally, the removal efficiency of NOx and CO/HC of the WCC or the UCC cannot but be affected by catalytic oxidation atmosphere due to oxygen (hereinafter, referred to as O2).
For example, the removal efficiency of NOx is highest in an acceleration section by activating the temperature of the WCC or the UCC, but when O2 remains in the WCC or the UC, a part of emitted NOx may be emitted without being purified. As such, the O2 is the largest cause of reduction in performance efficiency of the WCC or the UCC.
In particular, the catalytic oxidation atmosphere of the WCC and the UCC cannot but be most severe immediately after a fuel-cut ends due to the O2. The reason is that the NOx is emitted by engine combustion after the fuel-cut ends or the engine combustion is not made at the time of the fuel-cut and thus the O2 is completely stored in the WCC and the UCC. As the result, the catalytic oxidation atmosphere of the WCC and the UCC is most severe due to the O2 and therefore the purification of NOx cannot but start after a predetermined time elapses.
The fuel-cut is a method for reducing fuel consumption due to the stopping of fuel injection when deceleration happens during driving and is referred to as a fuel cut-off.
Therefore, the O2 converts the WCC or the UCC into the catalytic oxidation atmosphere and therefore cannot but be the largest cause of reduction in the removal efficiency of NOx and CO/HC.
As the method for removing the above problems, an O2 purge is used. In this case, the O2 purge is performed to remove the O2 based on a detection of an O2 sensor and thus may previously prevent the O2 from being excessively stored in the WCC or the UCC or the catalytic oxidation atmosphere from being formed in the WCC or the UCC.
Generally, an execution condition of the O2 purge uses a method based on a detection value of the O2 sensor which is installed before and after the WCC or an oxygen storage capacity (OSC) modeling based method.
Therefore, the exhaust system in which the WCC and the UCC are sequentially arranged performs the WCC O2 purge and the UCC O2 purge based on an oxygen storage capacity (OSC) modeling prediction value along with the detection value of the O2 sensor to again reduce the catalytic oxidation atmosphere of the WCC and the UCC which is most severely affected by the O2 at the time of the fuel-cut, such that the WCC and the UCC may remove the NOx emitted due to the combustion immediately after the fuel-cut ends.
However, a method for modeling an OSC quantity of the UCC by the UCC O2 purge is very difficult to accurately predict the OSC quantity and may not avoid the occurrence of a difference deviation in an OSC deactivation level during a mileage progress of a vehicle and in particular, may have a very difficulty in real application by not performing a periodic feedback.
To solve the above problem, the O2 sensor is applied to the UCC like the WCC and therefore the UCC O2 purge may be determined as a voltage value of the O2 sensor. However, when the UCC O2 purge starts and ends as the voltage value of the O2 sensor like the WCC O2 purge, the UCC like the WCC cannot but perform rich combustion until the O2 purge is completed and thus the generation of emissions such as CO and HC cannot but be increased instantly.
In particular, in the exhaust system layout in which the UCC is arranged after the WCC, the emissions such as CO and HC generated in the WCC are introduced into the UCC and may be removed by the UCC, but the emissions such as CO and HC generated in the UCC are not removed by the UCC and therefore cannot but be completely emitted to the air.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.